Field of the Invention
The present invention refers to a radar filling level measuring device for non-contact measurement of a filling level in a vessel or the like by means of microwaves.
Such radar filling level devices are mainly used for continuous filling level measurement as well as for limit level measurement of filling levels of any desired kind of filling matter in vessels, such as reservoirs. Filling level measuring devices of the above kind, however, might also be used for measuring the height of a liquid level of a fluid medium such as a watercourse. In that case the device should be disposed above the watercourse under a bridge or in any other way. In the present case, the term “vessel” should also embraces such environmental conditions.
The filling matter can be present either in solid or in liquid form, or may be a mixture of the two. The determination of the filling level is done using radar signals, i.e. microwave signals, in particular very short microware pulses.
In short, the present device works as follows: signals (short microwave pulses or frequency modulated microwave signals) are generated in an electronics unit and transmitted via an antenna unit in the direction of the surface of the filling matter to be measured. These signals are reflected on the filling matter surface and received by the antenna unit. The filling level can be determined using the delay of the signals.
Description of the Related Art
Usually, radar filling level measuring devices are formed to be attached in or on a vessel in such a way that the antenna itself extends through an opening in the vessel cover. The housing containing the electronics unit is arranged outside of the vessel as a matter of principle. As possibilities for attaching the radar filling level measuring devices, principally, flange and screw thread attachments are used. The flange attachment is characterized by the radar filling level measurement devices having a plate-like flange having through bores and having a connecting section extending through its central opening connecting an electronics unit of the radar filling level measuring device with the transmitting and receiving antenna. Electronics unit here refers to that portion of the filling level measuring device which generates at least the signals to be transmitted and radiated from the antenna unit in the direction of the filling matter. The attachment flange may be placed on top of a corresponding vessel flange of a vessel nozzle and screwed to it. In the screw thread attachment, the radar filling level measuring device often has a screw thread on a circumference thereof (external screw thread) which is to be screwed into a vessel opening having an internal thread.
Both types of attachment have certain common features. Both with the flange attachment and with the screw thread attachment, the electronics unit and the antenna unit are on different, opposing sides of a vessel wall. In both attachment types, the housing only serves to house the electronics unit; the separate antenna unit is always connected to this housing.
At the connecting point between the antenna unit and the housing, normally at least one connecting seam is formed having to be sealed using suitable sealing means. Since this connecting or sealing seam is situated within the vessel, it is exposed to the vessel atmosphere and must therefore be designed to be correspondingly resistant in order to ensure vessel tightness. Furthermore, with the present attachment types, all antenna units often have the problem that they tend to be soiled, the soiling being caused by the filling matter present in the vessel since they are always disposed on the inside of the vessel.
In fact, such radar filling level measuring devices have very often been used in chemically aggressive environments or in the food industry. Thus, in order to protect the antenna units from soiling and possibly against chemical or mechanically abrasive aggression, it is known in the prior art, to surround it with a solid layer of dielectric material (e.g. PP, PVDF, PTFE) or to only fill the funnel of an antenna horn element with such a material. Such radar filling level measuring devices have been manufactured and marketed for example by VEGA Grieshaber KG under the trade designation “Vegapuls 41” or “Vegapuls 43”.